The present invention relates to the field of cellular telephony, and more particularly to the transmission of information from a cellular network to a mobile station concerning handover between cells using different radio access technologies, such as from a cell using a radio access technology according to the Global System for Mobile communications (GSM) to a cell using radio access technology according to the Universal Mobile Telephone System (UMTS) Terrestrial Radio Access Network (UTRAN).
In a cellular network including different cellular systems, such as GSM and UMTS, which uses so-called wideband code division multiple access (WCDMA) and for which access is provided by UTRAN, to make a GSM to UTRAN handover/cell re-selection for a mobile station fast enough, i.e. to make a suitably fast handover from GSM, the current radio access technology (RAT), to UTRAN, the target RAT, it is necessary to transfer various items of information including so-called channel preconfiguration parameters from the target cellular network to the mobile station. For what are called hardcoded or static preconfigurations, standards specify the preconfiguration parameters, i.e. standards provide a certain number of sets of values of the preconfiguration parameters, each set of values defining a configuration. Examples of preconfiguration parameters are parameters indicating transport block size, transport block set size, spreading factor, CRC, and TTI (transmission time interval) value. Because the static preconfiguration parameters are specified in the standards, a mobile station can be expected to know the parameters (i.e. their values) for each static preconfiguration, usually maintaining the static configurations in memory. In addition to static preconfigurations, however, there are what are called dynamic configurations. These are usually information about the operation of the target RAT in addition to what is provided in any of the static preconfigurations. However, a dynamic configuration can also be complete in and of itself, i.e. it can specify all of the configuration parameters of the target RAT by itself, instead of supplementing the information provided by a static preconfiguration, and so by itself completely specify the configuration of the target RAT.
Unlike for static preconfigurations, the sets of preconfiguration parameters making up a dynamic configuration (whether it supplements a static preconfiguration or is intended to be complete by itself) must be provided to the mobile station dynamically, i.e. at or near the time of handover of the mobile station from GSM to UTRAN.
Section 13.7 of TS25.331 v.3.7.0, entitled Parameter Values for Default Radio Configurations, defines (static or hardcoded) preconfigurations, referring to them as default configurations. In section 13.7, the required parameter values are specified for each (hardcoded) preconfiguration. The UE maintains these (hardcoded) preconfigurations in memory.
System Information Block (SIB) type 16 defines dynamic configurations, which are referred to as predefined configurations in section 13.7 of TS25.331. SIB type 16 contains radio bearer, transport channel, and physical channel parameters to be held in memory by the UE. System information is specified to contain a preconfiguration identity and a value tag to identify a certain dynamic configuration as well as updates to dynamic configurations, if needed.
WCDMA is the most widely adopted air interface for so-called third generation wireless communication systems, where GSM is the corresponding interface for so-called second generation (i.e. digital) wireless communication systems. (First generation systems are analog.) In the context of the 3rd Generation Partnership Project (a joint standardization project of the standardization bodies from Europe, Japan, Korea, China and the United States of America), WCDMA is referred to as UTRA (Universal Terrestrial Radio Access), and can be either WCDMA FDD (frequency division duplex) or WCDMA TDD (time division duplex).
In UTRA the data generated at higher layers is carried over the air interface through transport channels, which are mapped to different physical channels in the physical layer. Two types of transport channels exist: dedicated channels (each identified by a certain code on a certain frequency and so reserved for a single user) and common channels (a resource divided between all or a group of users in a cell). There are a number (currently six) of different common transport channel types defined for UTRA, one of which is the so-called broadcast channel (BCH), which is used to transmit information specific to the UTRA network for a given cell. Associated with the BCH (a physical transport channel) is a logical channel, referred to as the broadcast channel (logical channel) and designated as BCCH. For clarity, the corresponding transport channel, designated as BCH, is referred to as the broadcast channel (transport channel).
The Primary Common Control Physical Channel (Primary CCPCH) is the physical channel carrying the Broadcast Channel (BCH). It needs to be demodulated by all the mobile stations in the system. As a result, the parameters with respect to (for example) the channel coding and spreading code contain no flexibility, as they need to be known by all terminals made since the publication of what are called the Release-99 specifications. The contents of the signaling messages have room for flexibility as long as the new message structures are such that they do not cause unwanted or unpredictable behavior in the mobile stations deployed in the network.
The logical channels are mapped to the physical channels in what is called the media access control (MAC) layer. A set of logical channel types is defined for the different kinds of data transfer services offered by the MAC layer. Each logical channel type is defined by the type of information transferred. There are two general categories: logical control channels, used to transfer control information, and logical traffic channels, used to transfer user information. The BCCH is a logical downlink (from base station to mobile station) channel used for broadcasting system control information. The BCCH is mapped to (connected to) the BCH (physical channel) in the MAC layer. (It may also be mapped to what is called the FACH, i.e. the forward access (physical) channel.)
It should be noted that the terms UMTS BCCH and UMTS BCH represent the same channel in UMTS. The term BCCH is used to point to the logical channel, while the term BCH is used to point to the actual transport channel being carried on the Primary CCPCH as described in 3 GPP TS 25.211, v. 3.4.0, sections/chapters 4-6.
GSM BCCH capacity is limited, and is not a suitable means for transferring additional (dynamic) preconfiguration parameters to a mobile station. However the transfer might be done, it is advantageous to keep the mobile station power consumption as low as possible. Therefore, when dynamic configurations are transmitted on the UTRA BCCH, it is necessary for example that these dynamic configurations be repeated in the system information of the UTRA BCCH often enough so that the UE need not continue to decode the UTRA BCCH for too long a time. In other words, the UE should not have to wait too long for the dynamic configurations to appear again. On the other hand, the UE should not attempt to decode the UTRA BCCH when UTRAN quality (coverage) is poor or if dynamic configurations are not used in the network. Unnecessary decoding of UTRA BCCH increases the idle mode activity of the UE and so increases power consumption.
The standard set out in the specification entitled, 3 GPP 25.302, v. 3.60, chapter 7, describes certain channel transport format combinations (TFCs) (which are supported by at least some mobile stations). In addition, there is a proposal from Vodafone (R2-002015) in which additional (dynamic) preconfiguration parameters are transferred from a cellular network (i.e. a base station) to a mobile station, but the proposal does not indicate how the transfer could be done fast enough (and also reliably enough) to provide for handover/cell reselection with acceptably low power consumption by the mobile station. Moreover, the prior art does not teach how to avoid so-called ping-ponging (handover/cell reselection back and forth from one system to another) in inter-RAT (Radio Access Technologies) cell reselection, i.e. in selecting between for example GSM and WCDMA (UTRA).
What is needed is a method for quickly and reliably communicating to a mobile station in being handed over from a cell operating under GSM to a cell operating under UTRA (WCDMA) any dynamic configuration information needed by the mobile station for operation in the cell operating under UTRA.
Accordingly, the present invention provides a method for a mobile station and a base station to which the mobile is being handed over, and corresponding apparatuses for use by the mobile and the base station. The method for use by the mobile station is for determining whether dynamic configurations are in use by the base station to which the mobile is being handed over, the base station to which the mobile is being handed over being of a first wireless communication system (such as the universal mobile telephone system terrestrial radio access (UTRA)) and the base station doing the handing over being of a different wireless communication system (such as the global system for mobile communications (GSM) wireless communication system). Both base stations are assumed to broadcast control signals on a respective broadcast control channel. The method for use by the mobile station includes: a) a step of determining whether the signal level of the control signal broadcast by the different wireless communication system meets a predetermined criterion for intersystem reselection; b) a step of receiving the control signal broadcast by the first wireless communication system; c) a step of performing an error check of the received control signal broadcast by the first wireless communication system; and d) a step of decoding the control signal broadcast by the first wireless communication system and in so doing, reading whatever dynamic configurations are being broadcast by the base station of the first wireless communication system; wherein, if the error check fails, the mobile station performs a step of waiting a predetermined time interval, and then repeats the method beginning with the step of receiving the control signal from the first wireless communication system.
In a further aspect of the invention, the mobile also performs a step of decoding the control signal broadcast by the different wireless communication system and reading a flag bit indicating whether or not the base station of the first wireless communication system is using dynamic configurations, and then only if the flag bit indicates that the base station of the first wireless communication system is using dynamic configurations does the mobile station receive and decode the control signal broadcast by the first wireless communication system carry out the aforementioned steps (a)-(d).
The corresponding method for use by the base station of the first wireless communication system in determining whether or not to use dynamic configurations in communicating with the mobile station being handed over by the base station of a different wireless communication system, assumes that the mobile station communicates with the base station of the first wireless communication according to a protocol in which a transport format combination indicator (TFCI) is used (at least by the mobile), and includes: a) a step of transmitting to and receiving from the mobile station with using dynamic configuration parameters; b) a step of examining the uplink TFCI to determine whether the TFCI points to a dynamic configuration; and c) a step of continuing to transmit to and receive from the mobile station with the dynamic configuration pointed to by the uplink TFCI, if the uplink TFCI points to a dynamic configuration, and otherwise a step of transmitting to and receiving from the mobile station using a static preconfiguration.
From another perspective, the invention includes a method and corresponding apparatus for use by a mobile station including the steps of: a) receiving at a mobile station a broadcast control signal issuing from a base station to which the mobile station is being handed over by another base station; and b) based on an error check of the broadcast control signal, either reading any dynamic configuration indicated by the broadcast control signal or waiting until a predetermined time to repeat the aforementioned step (a). In some applications, the steps (a)-(b) are performed only if a flag bit received from the base station handing over the mobile station indicates that dynamic configurations are in use at the base station to which the mobile station is being handed over.
From this other perspective the invention also includes a corresponding method (and corresponding apparatus) for use by a base station, including the steps of: a) receiving at the base station a signal from a mobile station indicating a dynamic configuration or a state preconfiguration in use by the mobile station; and b) using dynamic configuration parameters or static preconfiguration parameters in said base station depending on said signal received from said mobile station.
The present invention is an improvement over what is provided by the prior art in that with the present invention it is possible to avoid complex double cell reselection criteria based on some prioritization depending on whether dynamic configuration parameters are available or not.
In a concept proposed by Vodafone, a mobile station should give priority to GSM over UTRA if the mobile station has not been able to receive dynamic configurations even though the UTRA network is transmitting them on the UTRA BCCH. On the other hand, UTRA should be given priority over GSM if the dynamic configurations are not obtained by the mobile station. If this kind of prioritization is used in cell reselection, it should be taken into account in the cell reselection criteria of both GSM and UTRA in order to avoid having a mobile station change back and forth between radio access technologies. If prioritization is for example only defined in the cell reselection criteria of the GSM specification, it might happen that the prioritization rules in cell reselection criteria tends to push a mobile station toward using UTRA. However, since such complex prioritization cell reselection rules are not defined in the UTRA specification, a mobile station would immediately come back to GSM and then again to UTRA and so on. Instead of having such different kinds of prioritization rules in the cell re-selection criteria, the invention defines a mechanism to recover from a situation where the UTRA network uses dynamic configurations (transmitting them on UTRA BCCH as well), but the mobile station has not been able to receive them from UTRA BCCH due to poor UTRA signal quality or because the mobile station has been in GSM dedicated mode and does not have a dual receiver for receiving both GSM and UTRA data simultaneously.
Complex cell re-selection criteria (rules) both in GSM and in UTRA are required to make the concept work properly and to avoid ping-ponging between two radio access technologies (i.e. in this case between GSM and UTRA).
In addition, mobile station power consumption can be decreased using the invention, since according to the invention, a UE periodically looks for dynamic configurations only if the signal level of the measured GSM signal is either above or below a predetermined threshold (depending on the implementation) based on the measurement criterion for cell reselection defined between UMTS and GSM. Thus, the network operator can control terminal power by setting the threshold so that the UE need not attempt to read dynamic configurations when the signal quality of the UTRA network is not adequate.
Finally, the network can choose to use either dynamic configurations or (hardcoded, i.e. static) preconfigurations, depending on what sort of configurations the network supports and what services the operator would like to provide.